Method for reducing data in the transmission and/or storage of digital signals of several dependent channels

• US 5,812,672 A
• Filed: 12/15/1994
• Issued: 09/22/1998
• Est. Priority Date: 11/08/1991
• Status: Expired due to Term

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Herre, Juergen, Seitzer, Dieter
• Primary Examiner(s): Kuntz, Curtis A.
• Assistant Examiner(s): NGUYEN, DUC MINH
• Application Number:
  US08/211,547
• Time in Patent Office: 1,377 Days
• Field of Search: 381/1-2, 381/106, 381/29, 381/30, 381/17-19, 381/22-23, 381/107, 358/408, 333/14, 395/2.12, 395/2.14, 395/2.38
• US Class Current: 381/2
• CPC Class Codes: H04H 20/88 Stereophonic broadcast systems multiplex system in general H04J
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

A method for reducing data during the transmission and/or storage of the digital signals of several dependent channels is described in which the dependence of the signals in the channels, e.g. in a left and a right stereo channel, can be used for an additional data reduction. Instead of known methods such as middle/side encoding or the intensity stereo process that lead to perceptible interference in the case of an unfavourable signal composition, the method according to the invention avoids such interference, in that a common encoding of the channels only takes place if there is an adequate spectral similarity of the signals in the two channels. An additional data reduction can be achieved in that in those frequency ranges where the spectral energy of a channel does not exceed a predeterminable fraction of the total spectral energy, the associated spectral values are set at zero.

Claims

1. Method for diminishing cross channel interference in a data reduction process during the transmission and storage of information in N dependent channels, each channel comprising a channel signal having a frequency range which includes a plurality of frequency range parts, in which method scanning values of said channel signals in the time domain are transformed blockwise into the frequency domain, thereby providing respective spectral values for said range parts, the spectral values are encoded, transmitted and/or stored, decoded and transformed back into N channel signals in the time domain, comprising:

determining a single quantity which is a measure of the overall spectral separation between the different channel signals, based on the spectral values for corresponding blocks of the different channel signals;

comparing the quantity with a predetermined threshold;

performing common encoding of said channel signals when the quantity falls below the threshold; and

performing separate encoding of said channel signals when the quantity exceeds the threshold.

2. Method according to claim 1, further comprising determining the spectral distance between the signals of different channels from corresponding frequency domain parts of the signals.

3. Method for reducing data during the transmission and/or storage of digital signals from N dependent channels, in which scanning values of signals from the time domain are transformed blockwise into the frequency domain in spectral values, the spectral values are encoded, transmitted and/or stored, decoded and transmitted back in N channels in the time domain, comprising:

determining from the spectral values of corresponding blocks of the different channels a quantity which is a measure for the spectral distance between signals of the different channels;

comparing the quantity with a predetermined threshold;

performing a common encoding of the signals from the different channels upon the quantity dropping below the threshold;

further comprising determining the spectral distance between the signals of different channels from corresponding frequency domain parts of the signals; and

further comprising transmitting signals from two acoustic stereo channels and wherein the condition for the common encoding of the signals is described by the following rule

space="preserve" listing-type="equation">SD/SE<

c,

in which SD is a measure for the spectral distance between the signals from the right and left stereo channels and is formed according to the following instruction;

##EQU5## in which L_i or R_i are the coefficients of the left or right stereo channel frequency-encoded with the block length IBLEN, n is a freely selectable standard and f1 and f2 are the index limits of the considered frequency interval, the quantity LR_-- RATIO is the ratio of the signal quantities of the left to the right channel and SE the spectral energy of the stereo signal and which is formed according to the following instruction;

##EQU6## and c is a predeterminable threshold constant with 0<

c<

1.

4. Method according to claim 3, wherein the measure for the spectral distance SD is formed according to the following instruction:

##EQU7##

5. Method according to claim 4, wherein the threshold constant c is chosen between 0.5 and 1.

6. Method according to claim 5, wherein the common encoding takes place by a middle/side encoding and the quantity LR_-- RATIO is set at 1.

7. Method according to claim 5, wherein the common encoding takes place by intensity stereo encoding and for the quantity LR_-- RATIO the following applies:

##EQU8##

8. Method for reducing data during the transmission and/or storage of digital signals from N dependent channels, in which scanning values of signals from the time domain are transformed blockwise into the frequency domain in spectral values, the spectral values are encoded, transmitted and/or stored, decoded and transmitted back in N channels in the time domain, comprising:

determining from the spectral values of corresponding blocks of the different channels a quantity which is a measure for the spectral distance between signals of the different channels;

comparing the quantity with a predetermined threshold;

performing a common encoding of the signals from the different channels upon the quantity dropping below the threshold; and

further comprising determining from the spectral values of corresponding frequency domain parts of the different channels quantities which represent a measure for the spectral energy of these frequency domain parts, comparing these quantities of the different channels with the spectral energy of all the channels in these frequency domain parts and wherein in frequency domain parts in which the spectral energy in individual channels drops below a predeterminable fraction of the total energy of all the channels, the corresponding spectral values of the frequency domain parts are set at zero.

9. Method according to claim 8, wherein individual spectral values from the different channels are used for determining the spectral energy.

10. Method according to claim 8, wherein signals from two acoustic channels are transmitted, which are formed by matrixing from the signals of a left and a right channel of a stereo signal.

11. Method according to claim 10, wherein the matrixing is a middle/side encoding.

12. Method according to claim 11, further comprising replacing spectral values S in the difference channel (S_i =L_i -R_i) or in the sum channel (S_i =L_i +R_i) by the value zero in accordance with the following instruction:

space="preserve" listing-type="equation">if |S.sub.i |.sup.n <

k*(|L.sub.i |.sup.n +|R.sub.i |.sup.n),

space="preserve" listing-type="equation">then S.sub.i ;

=0

in which Lj or Rj are the coefficients of the left or right stereo channel frequency encoded with the block length IBLEN, n is a freely selectable standard and k is an appropriately chosen threshold factor, i running from 0 to the block length IBLEN exclusively.

13. Method according to claim 11, wherein for determining the spectral energy use is made of pairs of scanning values and the spectral values S_2i and S_2i+1, in the difference channel or in the sum channel are set to the value zero according to the following instruction:

space="preserve" listing-type="equation">if |S.sub.2i.sup.n +S.sub.2+1.sup.n |<

k*(|L.sub.2i |.sup.n +|R.sub.2i |.sup.n +|L.sub.2i+1 |.sup.n +|R.sub.2i+1 |.sup.n),

space="preserve" listing-type="equation">then S.sub.2i =0 and S.sub.2i+1 ;

=0,

in which the index i runs from zero to half the block length IBLEN exclusively.

14. Method according to claim 13, wherein the threshold factor k is chosen differently in different frequency domains.

15. Method according to claim 14, wherein in encoding the spectral values use is made of a psychoacoustic model for the calculation of a masking threshold and the threshold factor k is derived in adaptive manner from this masking threshold.

16. A method for diminishing cross channel interference in a data reduction process during the transmission and storage of digital signals from N dependent channels, the method comprising the steps of:

transforming blockwise scanning values of signals from the time domain into the frequency domain in spectral values, said spectral values being encoded, transmitted and/or stored, decoded and transmitted back in N channels in the time domain;

determining a single quantity which is a measure for an overall spectral separation between the different channels, based on the spectral values for corresponding blocks of the different channels;

comparing the quantity with a predetermined threshold;

performing common encoding of said channels when the quantity falls below the predetermined threshold; and

performing separate encoding of said channels when the quantity exceeds the threshold.